252

View of along a station platform with an automatic sign a 1 at t h e right Below - Motorman operating the release at an automatic signal Automatic Signaling, .Stop

RouTE No. 1 of the Chicago Subway system, placed in service in October, 1943, includes modern automatic block signaling, automatic train-stop equipment, and 3 all-relay route­ control . This Route No. 1, the first portion of a proposed ex­ tensive subway system, connects witl1 the North Side Elevated Lines near Armitage and Sheffield avenues, ex­ tends southeast in Clybourn avenue, east in Division street and south in State street to a connection with the South Side Elevated Lines near Seventeenth street, the total length of the double-track subway being 4.9 miles. Route No. 2, which is 3.85 miles long, connects with the North­ west Elevated Lines near Milwaukee and Evergreen avenues, extends southeast in Milwaukee avenue, east in Lake street, and south in Dearborn street, where it is to continue west in Congress street to a loop east of the river. This route No. 2, now about 80 per cent complete, wi ll be fini shed as soon as war conditions permit. Plans for future subways include al- 253

Automatic signaling for 40 each hour includes time­ dis t ance-speed con trois on decend­ ing grades and on approach to stations­ Three interlockings are· especially de­ signed fo r rapid change of line-up

Panel of the UR in­ terlocking machine at the South Portal includes four main tracks, the two center tracks for express trains and the two outside tracks for local trains. The subway is double track and all trains stop at all stations. In order that trains from any of the four tracks from the north can be routed to either track in the subway or vice versa, the track layout at the north portal was designed with crossovers and Route and switches, as shown in Fig. 2, in which the tracks from the subway emerge on an ascending grade as the Installed in the Chicago Subways two middle tracks, with two elevated tracks on each side. This layout in­ cludes 8 crossovers, 2 single switches and 34 signals, which are controlled most 42 miles of additional subways whereas the elevated crosses the river by an all-relay route-control ma­ to be constructed as finances become on a drawbridge, and quite often this chine in a tower at Armitage avenue. available. bridge has to be raised for the passage South of the south portal at Seven­ of a boat, with the result that trains teenth street, the South Side Ele­ Utilization of Route No. 1 operating on the elevated structures vated has three tracks, one track on are seriously delayed. each side is for local stops as well as The purpose for these subways is Since the subway was placed in for certain through trains, while the to extend local facilities, service, the traffic has increased rap­ center track is fo r through express expedite train movements and ulti­ idly, not only because of the improved trains between Seventeenth streetand mately to permit the removal of the service, but also due to the fact that Indiana avenue, this track being used elevated track structure in the down­ the rationing of tires and gasoline has in one direction or the other depend­ town area. The "L" trains now oper­ forced many persons to abandon ing on the preponderance of traffic ; ating through subway Route No. 1 automobile transportation and use the for example, northbound in the from the South Side Elevated to the rapid transit lines. morning inbound rush hours, or North Side Elevated and vice versa southbound in the evening outbound fo rmerly operated on the elevated Track Layout of Route No. 1 rush. In order that trains can be structure in the downtown area and routed in either direction between now save from 7 to 22 minutes daily Not all of the trains to and from the three-track elevated lines and for each of thousands of passengers. the south or the north use the new either the subway or the elevated A further advantage is that the subway, and, therefore, the track lay­ north of Seventeenth street, the track stations on the new subway are lo­ outs at the portals were designed layout is designed as shown in Fig. cated more conveniently with refer­ so that trains can be routed to or 3. This layout includes 4 crossovers. ence to important stores and office from either the subway or the ele­ 1 single switch and 17 interlocking buildings. ' Another is that the sub­ vated structure through the down­ signals, wh ich are controlled by an way goes under the Chi cago river, town area. The North Side Elevated all-relay route interlocking machine 254 RAILWAY SIGNALING May, 1944 in a tower north of Eighteenth street. mechanisms which are equipped with the train line thus causing an emer­ The details of the construction and electric locks, the control of which gency application of the brakes on operation of these interlockings will will be explained later. the entire train. be explained later in this article. The red aspect of any of the auto­ Where the subway under State Automatic Block Signaling matic block signals indicates Stop-and street turns east to connect with the Then-Proceed. When the train stops, elevated structure at Thirteenth The automatic block signaling in the motorman must lean out his win­ street, excavation was made arid bulk­ the subway is arranged for train dow to operate a stop release, mounted headed for a future extension south operation in one direction only, right- near the signal, which causes the trip under State street. The northbound tube of this future extension, built at a lower level to provide grade sep­ __/"-­ / - r aration, is equipped with a stub track / / with a Y connection to the present '\. // II tracks and can be used to double back +-o~" trains from the north. This track lay­ ...._

Fig. 1-Map of the Route No. 1 of the Chicago subways

South Portal, trains are ordinarily hand running on each track. The sig­ arm to be lowered to its normal posi­ operated right-hand running. In or­ nals are of the color-light type which tion, thus allowing the train to pass der to permit maintenance forces to display the conventional aspects red, without the brakes being applied. work on a section of track, all trains yellow or green. At each signal and in both directions can be operated on at rail level there is an automatic trip Track Capacity Determined by the other track during slack periods type which is in depressed Train Speeds, Spacing Between between 2 a.m. and 5 a.m. In order to position as long as the signal displays Trains and Braking Distances sectionalize the tracks for this pur­ either the green or the yellow aspect, The automatic signaling was pose, there are two sets of diamond but when the signal displays the red planned to attain two objectives ; to crossovers, one just south of the sta- aspect, the trip arm is raised to a level operate the trains at the maximum

Fig. 2-Track and signal plan of the interlocking at the South Portal tion at Grand avenue and the other where it will strike and operate an speeds which are practicable in con­ south of the station at North avenue. air valve on each car of a train, if the sideration of the spacing of stations These crossover switches are operated train is driven past the signal. Oper­ and the tractive effort of the equip­ by hand-operated switch-and-lock ation of this valve releases the air in ment, and also to get as many trains

--sn------_ ~ ~ 1:!! 42 ~ lli L~ ------~2o ~cc------4o-~- r-r 1 ~---- ~u=--.....,6:-::-zc- -:.Eo..w:!!o..subway ~ 18 28 J: :::::::=-:=:::: 44 :r .L.., 46 C 66 Tk.J ~16 __]---- 32C__ .;_ 1 -=I-:::.:IJ-0 -==-----,-+-_-4-=-=~----:=::-----:~=---~68 c· 10 1 1 I 1-1 I 1-1~ J4l J61 '5oTl "!154 '411 m Fig. 3-Track and signal plan of the interlocking at North Portal May, 1944 RAILWAY SIGNALING 255 over the line as possible by reducing an hour. On ascending grades the grades. In consideration of all these the space between trains to a mini­ train braking distance is shorter and, factors, the speed of trains when mum that is consistent with that re­ therefore, the block lengths can be descending grades is limited by rule quired to stop short of a train ahead. correspondingly shorter, thereby to certain maximums as marked on On this basis, for the normal run- automatically reducing the space be- signs along the track, and the signal-

~ ~ ~ ~ ~ ------D~--~d~----c=rO~----~c------~6~----~b~-----D------a------~ Fig. 4-Diagram showing control limits of signals and train stop ning speed between stations th e min­ tween following trains to compensate ing and train-stop system include imum spacing of signals is the di s­ for the reduced speed when ascending special grade-time-distance controls tance required to stop a train running the g-rade. arranged so that the brakes are ap­ at maximum speed with an emer­ plied automatically if this maximum oency application of the brakes, plus Descending Grade a Different speed is exceeded. The speed is meas­ ~ short distance as a factor of safety. Problem ured on the time-distance basis. When As mentioned previously, the train­ a train enters the block, the release stop arm at a signal is in the raised At North Portal, the line descends of the track relay starts the operation position only when the signal displays from the elevated structure to the of a time-element relay which is set the red aspect, which may be with a subway level, at a grade which, for to operate its cycle before the train train stopped just beyond the signal. the most part, is about 3.0 per cent. passes the next signal, if the speed is Therefore, in order to provide auto­ A similar grade extends where the 25 m.p.h. or less. matic train-stop protection for train subway tracks emerge and climb up braking distance, as shown in Fig. 4, to the level of the elevated structure Typical Grade Timing the second signal in the rear of the at South Portal. Also 3 per cent train is held at stop with its train-stop grade from each direction extends A typical layout for "grade-timing" raised to the tripping position. This down to the portion of the subway signaling is shown in Fig. 5. Nor­ means that the red aspect of each sig­ under the Chicago river. mally, i.e., with no train occupying nal is controlled not only for the If trains were allowed to operate the automatic blocks shown, the sig­ length of its own block but also by the at maximum speed when descending nals 14 and 13 display the red aspect, next one as well, this being termed these grades, the train stopping dis­ signal 12 yellow and lunar white, and one-block overlap signal control. tance would be much longer than on signal 11 the green. Signals 12 and Thus referring to Fig. 4, signal No. level track because of the effect of 13 are each equipped with a lunar 4 as well as No. 3 displa~ the reel gravity. Long blocks would increase white marker which is lighted only aspect and signal No. 2 displays the the space between trains and thus when the signal displays the yellow yellow aspect until the rear of the reduce the track capacity below the aspect and there is no train in the train passes signal No. 5. Therefore, fixed limit of 40 trains per hour. control limits of the next grade time if trains are to operate at normal Furthermore, from the standpoint of signal in advance. maximum speed on green signals, the safe train operation, the speed must As a train approaches the time sign minimum spacing from the rear of not be too high- when descending at signal 11 , the motorman should one train to the head end of the next must be equal to the total of the lengths of the four blocks, a, b, c, and d, and each of these blocks is at least equal to the train stopping distance plus a factor of safety. This total dis­ tance between trains reduces the num­ ber of trains which can be operated past a given point in a certain time.

Eight Cars To a Train

The design is for cars each 48 ft. 6 in. long, and for 8 cars to the train. Furthermore, the volu.me of passen­ ger traffic in rush hours established the ruling that the signaling should provide for the operation of trains on 90-second headway, i.e., 40 trains

View at switches of emergency crossovers showing T-21 man­ ually operated switch­ and-lock mechanisms with electric locks on the levers, as well as the clockwork time re­ lease and lamps on the case with door open 256 RAILWAY SIGNALING May, 1944 reduce the average speed of his train as for longer blocks at higher speeds. If the speed of the train is reduced so in block "a" to the limit posted on For this reason the uniforrn flow of that the head end does not pass the the sign, and if this is clone, the aspect traffic is not interrupted. next signal before the timing relay of sigJqaJ 12 will change from yellow completes its operation, then that sig­ to green before he passes it, and prior Approaching Stations nal will have its extended overlap to this, the train stop at signal 13 has control cut off, the train-stop will be been lowered and the aspect of that The duration of a train stop at a lowered to its non-tripping position signal changed from reel to yellow station varies from 20 to 60 seconds. and the signal will change . from the and lunar white. If this change does In the meantime, if trains are being reel to the yellow aspect so that the not occur, he knows that he must operated on a 90-second headvvay, the train can continue without stopping. make a further reduction in speed next train is approaching the rear of If this train continues at the re­ throughout block "b" so that his aver­ the train which is then standing at the stricted speed, the next signal will age for the two blocks ("a" and "b") station platform. Under these cir­ have its extended control cut off by wi ll be less than the posted limit. If cumstances, the desirable objective is the second timing relay, and so o1i. so, before he arrives at signal 13 the to provide for the approaching train thus bringing the train up closer to the train-stop trip will be lowered and the to keep moving at a gradually reduced station, so that as the leading train aspect will change first from reel to speed and then, as the train ahead departs, the second one can pull up to yellow and then, after signal 14 has departs, the second train can run on the platform at approximately the cleared, to green. On the other hand, into the- station and stop without hav­ same speed. Thus the capacity of the if the speed is not reduced according ing been required to stop and lose track as a whole throughout the length to posted limit and the train cannot time unnecessarily at a signal in ap­ of the subway is increased by de­ be stopped short of signal 13, then proach to the station. creasing the speed of a follo1ving the train-stop is effective in applying The signals in approach to a station, train, thereby reducing the spacing the brakes. Such occasions, however, called station-timing signals, are between trains in those sections where are very rare. The motormen soon spaced closer together with their con­ trains make regular stops. learn to gage the speed so that they trols overlapped to govern over sev­ When no train is occupying the can run very close to but not exceed eral blocks, so that a train standing station, the signals in approach to the the speed limit. and thus the aspect at a station platform is protected by station normally display the green

~6T ~GT a 14 13 12 II Fig. 5-Diagram illustrating grade-timing signaling changes to green just prior to the time three or more red signals, the total aspect. Therefore, under these con­ the head end of the train passes the distance providing safe braking dis­ ditions a train approaches at normal signal such as 12 in Fig. 5. 'tance at maximum speed. For ex­ speed. ample, in Fig. 6, the overall distance Track Occupancy Control from signal 21 to signal 24 is the full Time-Relays Driven by Code block length for train-stopping dis­ Transmitters If, as the train was approaching tance at maximum speed. signal No. 12, the lunar white marker In addition to the special overlap, The time-element relays are all of was not lighted in combination with the controls of these signals are ar­ the ratchet type, operating on 16 volts the yellow, this would indicate that ranged so that, with a train at the cl-c., and can be set to operate for any

<---- -*------1 Sfafion Timing signal confrols --E------Dcrsh lines show exfendecl confrols 24___ 2L I Oaf dash lines show iiming secfions «E-----. ------<------i -E------E------1 __1_2 __ 1 ~ ------E------j _l!__ --·I 1 25 1 24 1 23 1 22 1 21 ~ ~ST ~ST ~5T ~ST ~ 5T L."::.J"

Station Fig. 6-Station timing signal controls, the dash lines show extended controls and the dot lines show the timing sections signal No. 13 is displaying the red station, a second train can close in timing from 2 y; to 25 sec. or 10 to aspeCt because a train ahead is occupy­ under the authority of yellow aspects 120 sec. ing the track, and, therefore, that sig­ by reducing speed sufficiently so that The shorter range relay is cali­ ~al No. 13 will not clear regardless the train can be stopped if necessary brated in 2.5-second divisions, the ¢if how slow the second train is in the length of one of the short longer range relay in 10-second eli­ run. Based on this information, the blocks. An illuminated "T" sign in­ visions. Both relays are adjustable motorman is prepared to stop his forms motormen where the special for time interval by screw thread. train short of signal No. 13. With timing controls start so that they can providing micrometer adjustment for this form of control, the blocks on reduce the speed of their train ac­ fractions of a second. descending grades can be short cordingly. All of the time relays in an inter­ enough so that the time-distance of When a train enters each block, the locking, on a grade-time zone or in trains in such blocks is about the same operation of a timing relay is Btarted. both areas in approach to a station are ' May, 1944 RAILWAY SIGNALING 257 driven by a circuit fed from a pendu­ lum-type code transmitter which oper­ ates continuously from the 16-volt d-e. supply at the rate of 240 times each minute. The output of the code transmitter f,eeds bus wires extending throughout the limits of the station timing or grade zone. The timing­ Southbound train de­ relays and the code transmitter are of scending f r o m the the plug-in type and are the same out­ elevated s t r u c t u r e side dimensions as the other relays. to the subway at the North Portal plant Single-Rail Track Circuits

The energy for the motors on the cars is at 600 volts d-e., the positive side of which is connected to the , and the negative return is con­ nected to one of the track rails. The other track rail, called the signal rail, is cut into lengths by the use of ordinary insulated rail joints. Thirteenth street. Each plant includes versed to fo llo w the other train. As At the feed end of a track circuit, one two compressors, each rated at 150 soon as the first train passes signal wire from the secondary of a track cu. ft. per minute. Each of the two 30, the operator can "store" the con­ transformer is connected to the sig­ tracks in the subway is in a separate trol for the route from signal 12 via nal rail next to the insulated joint and tunnel and, therefore, a separate 10- crossover 3 reversed by pushing but­ the other wire is connected to the in. air pipe was required throughout tons 12 and 28. As soon as the rear of negative rail. At the relay end of the the length of each of the two tunnels. the first train clears the sectional circuit, one wire from the track relay, route release track circuit, the cross­ which is the a-c. vane type, is con­ Cable Distribution over will at once be operated to the nected to the signal rail next to the reverse position and signal 12 will be insulated joint, and the other wire is The automatic block signal line cleared accordingly. This "storage" connected to the negative rail. The circuits are No. 14 wire in aerial-type of control saves seconds at the right relays and transformers are protected cables. These cables, together with time to prevent unnecessary train from excessive propulsion current the 2-conductor cables for the 110- stops. by means of a resistance, unit and volt a-c. and the 16-volt d-e. power, 600-volt fuses inserted in the con­ are run on messengers on brackets on Interlocking Machines nections to the signal rail. One ad­ the walls of the subway tunnels and vantage of using this so-called "sin­ along under the station platforms. The interlocking machines and con­ gle-rail" type of track circuit is that All the relays are the quick-detach­ trols are of the "UR" Union Route no impedance bonds are required, and, able plug-in type which permits a type. The three plants are of the same furthermore, the exact ends of track relay to be replaced quickly without construction and, therefore, the fol­ circuits can be fixed without cutting changing wire connections. These lowing explanation will be confined rails too much. relays are housed in cases at the auto­ to the North Portal plant. matic signals. At the interlockings, The panel of the machine is 220 Power Supply and Distribution the relays are on racks in instrument in. high and 60 in. long· and is made rooms in the towers. of sheet steel treated with baked Electrical power equipment for enamel having a dull black surface. feeding the signal system is located 138 Tra ins an Hour The track and signal layout is repro­ at each of the three interlockings and duced in miniature on this panel, each also at eight intermediate points. Each Between 8 a.m. and 9 a.m. every track being represented by moulded of these power sources feeds a certain week day, there are 69 trains sched­ translucent glass sections, which are territory. At each source, duplicate uled northbound and the same num.ber fitted behind slots 3/16 in. wide cut transformers with automatic transfer southbound through the North Portal in the steel panel. When the plant is equipment in the secondary leads, sup­ interlocking. Three and sometimes normal, these sections of glass are not ply a two-wire single-phase 110-volt four or five trains are occupying the illuminated. signal power distribution circuit which plant limits including the approach Each signal is represented on the extends to all the signal and track cir­ sections. The route control system is , diagram by a symbol. Adjacent to the cuit feed locations on the given ter­ therefore, an important advantage in symbol for each interlocked signal, ritory. Also, in each power room there changing line-ups quickly. As a and on the line representing the track, is a set of rectifiers in multiple which special feature to permit new routes there is a push button, knovvn as a feed a 16-volt d-e. power distribution to be set "up automatically as soon as ro ute button. circuit which extends on two wires the rear of a departing train clears Thus there is a push btJtton for to each signal to feed control circuits, the release section involved, provis­ each signal where a route may start. as well as electro-pneumatic valves ions have been made for the "storage" these being known as route buttons. for switch machines and train-stop of controls. For example, a north­ In order to line up a route, the oper­ mechanisms. bound train coming out of the tunnel ator pushes the button corresponding Compressed air for operation of is using the route to the northward with the signal at which the approach­ the electro-pneumatic switch machines express hack via signals 16, 30 and ing train is to arrive at the plant. Thi;; and train-stop mechanisms is pro­ 48. Fig-. 2, and the next northbound action is indicated by the appea,rance vided by two compressor plants, one train from the elevated track No. 3 of a red light at the side of this but­ at North Portal and the other at is to be routed via crossover 3 re- ton. Then he pushes the button at the 258 RAILWAY SIGNALING May, 1944 entrance route button 16 and then pushes exit route button 66, Fig. 2. After all the switches are properly positioned, all of the signals will clear, including 16, 30, 48. This obviates the pushing of route buttons 30 and 48, and is known as through routing. A through route can also be estab­ lished by pushing entrance button 16 and exit button 68. The interlocking signals for the normal directions of traffic each have two signal heads and a third unit at the bottom, which is a normally extinguished yellow lens. The as­ pects in the top head apply in general to the straight-track route, the aspects Train stop mechanism and trip of the second head apply to the diverging routes. The display of a proceed aspect in either the top or exit light on the line representing the ing and turning the entrance route the second head depends not only on track on which the train is to depart button. In order to cancel this con­ switch position but also on non­ from the interlocking limits. This trol, the button must be turned to occupancy of the tracks in the route. initiates actions which control the normal position and pulled out mom­ If all the switches have been posi­ switches and crossovers to be operated entarily. tioned properly for a route by pushing to the positions called for to complete an entrance button and an exit but­ the route. The track sections repre­ Through Routing ton, but the signal does not clear due senting the switches, which are al­ to an occupied track section, a yellow ready in the position called for, will When a train is to make a move call-on aspect can be displayed on the be lighted white, whereas those repre­ through the plant on express tracks, third "arm" of a high signal, by also senting switches to be operated will the route can be established by push­ pushing the call-on button corre­ flash red until the switches are over ing the first entrance route button and sponding with the signal. These call­ and locked, then the indicating sec­ the last exit route button. This is on buttons are in a row above the tions will be lighted white. Thus called through routing in contrast track and signal diagram. A special when the track line up is complete, the with requiring that the button for feature is that when the call-on as­ route is indicated by a continuous each_signal on the route be pushed. pect is displayed, this fact is indicated illuminated white line. Then the sig­ For example, when making a move by a flashing white light rather than nal clears, which is indicated by the from the northward track in the sub­ a steady white light at the entrance lamp at the side of the entrance route way to the northward express track route button. A call-on line up is can­ button changing from red to white. on the elevated, the operator pushes celled by pulling the entrance route Track sections of the diagram representing a switch are flashed white when an approach signal lock­ ing this switch indicates clear or when a train is occupying the extended locking sections of the switch. As the train accepts the signal and passes through the plant limits, the lights in the separate sections of the track diagram change from white to reel as the train occupies each of the corresponding track circuits, and after the rear of the train clears any given circuit, the light in the corresponding indicating section is extinguished, un­ less non-stick control is in effect, in The plug - in type which case the sections again show relays can be re­ white. placed quickly and Routes which are initiated by push­ with nowirechange ing the entrance route button and the exit route button are under "stick" control; i.e., such routes are auto­ matically cancelled when a train ac­ cepts the signal and passes through the plant. On the other hand, if a cer­ tain route is to be used by two or more following trains, "non-stick'' control can be established so that the signal will again clear for each suc­ ceeding train without any action on the pctrt of the operator. This "non­ stick" control is established by push- May, 1944 RAILWAY SIGNALING 259 button. This call-on control applies returned to the control of the route also to all of the reverse-traffic dwarf system by placing the lever in the signals. center position. If a track circuit failure causes the Signal Take-Away electric locking to be effective in pre­ venting the operation of a switch by If a route has been established and ordinary means of control, a special the signal cleared, but this route is form of emergency release and con­ to be taken away without having been trol may be used. All home signals, used by a train, this result is accom­ dwarf signals and approach signals plished by pulling th~ entrance route governing routes including the said button. Then the white light at the switch are placed in the Stop position. button, as well as the continuous white Next the auxiliary switch control line of light on the track diagram, lever for that particular switch is are extinguished . However, if a train thrown to either the normal or the is approaching the signal when the reverse position depending on which route is thus cancelled, the approach position of that switch is desired. locking takes effect, and the continu­ Then the operator breaks the seal on ous white line of light on the diagram the emergency release button directly persists for a period of approximately under the said auxiliary switch lever 20 seconds, thus indicating that the by pushing in the button, after which route is locked for that period of time, the button is pulled out and held until and, therefore, no conflicting route the switch operates to the position to can be established. correspond with the position of the Time locking rather than approach auxiliary lever, which will be indi­ locking is provided for all dwarf sig­ cated on the panel. Pulling 'the lever, nals. If a route button controlling a after being pushed, starts a time­ dwarf is pulled, the continuous white element release which is adjusted to line of light on the control panel wi ll operate in about 30 seconds, after persist for approximately 20 seconds ; which the switch will operate. i.e., until the time-element relay oper­ After the switch lever has been ates to release the locking. placed on center, the route control Ground detector relays and lamps A special feature of this interlock­ buttons can be used to establish the ing is that the approach signals are remainder of the track line up and crossover track circuit, tht:ough nor­ semi-automatic, this being arranged clear the signal, which would be the mally-closed contacts that check the so that the towerman can stop a train call-on signal if a track circuit is out normal position ·of the switch, the at such a signal. The signals 4, of service. locked position of the lock plunger, 10, 34, 36, 38, 56 and 62 can each and the normal positioh of the hasp be cleared by its respective con­ Control of Hand-Throw Crossovers controller, so that if the switch ped­ trol button without the use of an exit lock is removed, the control circuits button. If such a button is turned As previously mentioned, a set of are open. The clockwork release must when in the pushed position, the con­ diamond crossovers is located south be turned by hand to return it to the trol is non-stick so that the signal will of the Grand Avenue station and an­ wound position in order that the door again clear after a train proceeds other set is located south of North of the case may be closed. beyond the track circuit control limits. Avenue station. The switches of Chicago's first subway was de­ When a switch is being inspected these crossovers are each operated by signed and constructed under the or adjusted it can be controlled in­ a Union Switch & Signal Company supervision of Philip Harrington, dividually by a separate lever rather Model T21 hand-operated switch- Commissioner of the Department of than by the route control system. For . and-lock mechanism, equipped with an Subways and Super-highways. The this reason, individual control levers electric lock which locks tbe switch automatic signaling and interlocking for the switches and signals are pro­ operating lever in the normal position. was planned and installed under the vided on the panel below the track All four of the electric locks at a direction of C. W. Post, Electrical diagram. A special feature of these diamond crossover layout are con­ Engineer, assisted on signaling mat­ switch levers is that they are of the trolled by one clockwork time re­ ters bv ·walter vV. Wenholz of his three-position type, normally they lease, which is mounted in a case with office,' as well as by R. N. Wade, stand on center in which position they lamp indicators. ·when the door of Engineer Maintenance of Way and are ineffective in controlling the this case is opened, a switch is closed C. A. Butts, Assista11t Signal Engi­ switch, and, furthermore, these levers to feed energy to the indication lamps. neer, of the Chicago Rapid Transit must be in the center position in order If no train is approaching within cer­ Company, which cop1pany operates. for the route control to be used. A tain approach limits on each track, the subways. The Federal gov.ern­ lever is operated to the left to control the corresponding indicator lamps are ment shared the cost of the project its switch to the normal position or lighted. The clockwork release is and otherwise co-operated with the to the right to control it to the reverse turned by hand to release it. This city through a special Subway Com­ position. In order for this lever con­ action places the signals in each direc­ mission of which Joshua D'Esposito trol to be effective. all route controls tion to their most restrictive aspect. was P.vV.A. project engineer. The affecting the switch must have been After the release runs down, which major items of signal and interlock~ cancelled, and all home signals lead­ requires 1 minute, the electric locks ing eq uipment as well as circuit plans, ing to routes over the switch must, on the switches are released. The key were furnished by the U ni on Switch of course, be in the Stop position, and for the switch padlocks is sealed in & Signal Company, and the wire a,nd its detector locking sections free. the time release case. cable -in connection with the sigmillng When the work on the switch has The signal control circuits check was furni shed bv the Kerite Insulated been completed, the switch can be through the front contacts of a special \\' ire & Cable Company.